Summary of Work: Mutational spectra provide information to help understand mechanisms underlying mutagenesis and carcinogenesis. We will examine forestomach tumors induced by a class of carcinogens (chloroprene, isoprene, and 1,3-butadiene) for activating mutations of the ras gene. This information will then be related to the known mutagenic properties of exogenously and endogenously-induced DNA adducts to provide information about the relevance of different adducts. Since these carcinogens induced tumors at multiple sites, mutational spectra for the other sites will be compared to that for the forestomach to determine whether a similar mechanism is involved.